Lawo w995-1 gain mod and noise problem

[duende]

Hi,

At the moment i'm testing a Lawo W995-1 for mastering applications. Il love the eq tone and curves but i want to be sure i can solve some problems before to buy it.

The unit is noisy at high frequencies and one channel way more than the other. This channel is less noisy when :


- I push  -2db 1.5Khz the noise disappears ( become as the other channel ), i bypass the channel, unbypass the channel and the noise reappears , with same settings...

- The PSU is a cheap Smps, i think a linear power supplie can reduce HF noise, but why  a channel more than the other ?

- I would like to mod the gain, not sure what gain range i want at the moment but divide all the gain range by 2 it's maybe the simplest way ?

- The amphenol relays are not working correctly, i have to change them, but if i "bypass" the bypass section, relays, opamp... maybe can i reduce moise ?

- What the beneficial to change the single power supplie to symetrical psu ?



The schematic is for the Lawo 995-3 but i think they are identical.

Thanks

 

[abbey road d enfer]

- The PSU is a cheap Smps, i think a linear power supplie can reduce HF noise, but why  a channel more than the other ?

First you need to test with a clean linear supply. Then you need to check the regulated voltage (at the collector of the BD436 or C11), with a scope. But noise can be attributed to a defective opamp, more likely.

- I would like to mod the gain, not sure what gain range i want at the moment but divide all the gain range by 2 it's maybe the simplest way ?

Do you mean changing the cut/boost range? If that's what you want, you need to change all the resistors and caps wired to the switches. Good luck with that!

- The amphenol relays are not working correctly, i have to change them, but if i "bypass" the bypass section, relays, opamp... maybe can i reduce moise ?

Not very likely.

- What the beneficial to change the single power supplie to symetrical psu ?

None worth the hassle. The opamps may not be operable with more than 24V.

 

[duende]

Thanks !

The unit is not mine so i don't want to mod it right now.

Really is it not possible to mod gain range without changing all switch resistors and caps ? Is it due to inductor topology ?

Changing resistors it's possible but find values and change caps it's another story ...

Maybe run the unit in parrallel is a good option.

 

[abbey road d enfer]

Really is it not possible to mod gain range without changing all switch resistors and caps ? Is it due to inductor topology ?

No. The LF and HF range are governed by the resistor/cap values around S1 and S2.
It may be possible for the midrange by altering R32-36.

 

[duende]

Thanks Abbey road d'enfer